Angular accelerometer



Oct. 20, 1953 T. w. SHEPPARD 2,656,519

ANGULAR ACCELEROMETER Filed Aug. 31. 1950 2 Sheets-Sheet 1 F I6. I

INVENTOR.

THOMAS W. SHEPPARD my MM ATTORNEY Oct. 20, 1953 Filed Aug. 51, 1950 2 Sheets-Sheet 2 i I IO :1 I!

I I 15 I FIG. 6

I I INVENTOR.

E THOMAS w. SHEPPARD BY L jzMM ATTORNEY Patented Oct. 20, 1953 UNITED. STATES PATENT OFFICE AN GULAR ACCELEROMETER Thomas Weliborn Sheppard,v Sandy Spring, Md., assignor to the United States of America as represented by the. Secretary of the Navy Application August 31, 1950, Serial No. 182,447

8 Claims. 1

or rocket propulsion, were too severe to permit correct readings to be taken. Moreover this type of accelerometer employed a viscous liquid as a damping component, which necessitated fluidtight construction and was subject to trouble from the possibility of leakage. 'Ihe'present invention incorporates magnetic damping, due to eddy currentsproduced in a non-magnetic metal element carried by a movable member of the accelerometer.

An object of the invention, therefore, is to provide an adequately sensitive accelerometer that is responsive to angular acceleration, and that nevertheless is rugged enough to withstand the shock and vibration encountered in guided missiles.

Another object isto provide simple but effective damping means in an angular accelerometer that is free from liquids.

A further object is to provide an angular accelerometer wherein the angular acceleration is measured as the variation of an inductance.

Other objects and many of the attendantadvantages of this invention will be appreciated readily as the same becomes understood by reference to the following detailed description, when considered in connection with the accompanying drawings, wherein:

Fig. 1 is a plan of an accelerometer embodying the invention;

Fig. 2 is a section in the plane 2-2 of Fig. 1, small portions being shown in elevation;

Fig. 3 is a bottom view on an enlarged scale, partly broken away and in section;

Fig. 4 is a section through the accelerometer, on a further enlarged scale, in the plane 4l of Fig. 2;

Fig. 5 is a section in the plane 55 of Fig. 2, a portion of the frame of the device being shown in elevation;

Fig. 6 is an end elevation, partly in section; and

Fig. 7 is a detail or an adjusting, lever.

Referring first to Figs. 1 and 2, the device comprises an elongated frame I whichhas=alongitudinally located slot 2 therein in which is pivotally mounted a lever 3'. The frame I may be- .secured to the object whose angular acceleration is to be determined, for example, a wall 4 of a missile or other vehicle, as by screws la. The lever 3 constitutes the element of the accelerometer that responds to the angular acceleration: and must be shaped properly and mounted accurately. A it is desirable'thatthe lever 3 should be very light and yet have a considerable moment of inertia, all superfluous metal is removed from it, except at the pivot and at its two ends by making. it of I-beam cross-section. At its right-hand end, as shown in Fig. 3; the lever l carries an armature plate 6 of form-magnetic material. secured by a screw 1; A best shown in Fig. 3, the plate 8 is preferably rectangular.

At is left end (in Fig. 3) the lever S'carriesa cup 9 made of metal having good electrical conductivity, preferably copper. said cup being held to the lever 3 by a screw 8. The cup 9 co-- operates. with a permanent magnet So having a magnetized core Ill of cylindrical shape, a U.-

8 to I5 inclusive, is adjustably secured to frame I by screws 44 and constitutes the magnetic damping means.

As shown in detail in Fig. 5, the frame I has at its right-hand end a tubular lug 5. is internally threaded at I6, to receive the correspondingly externally threadeclcasing of an "E- core and its transformer windings. This is a core I! made of E-shaped laminations carrying the windings I8 and I9 which, as shown in Figs. 1 and 2, have one common tap or terminal 20 and two individual outer terminals 2 I' and 22,.for connection into a suitable oscillator circuit, not

shown. The core I! is secured in a tubular externally threaded casing 23, that fits. in the. lug 5, and may be adjusted longitudinally by means of said threads. However, as the core-ends must.

aline with the armature plate 6. so that. the.

This lug E-core and armature jointly may constitute a variable inductance assembly, it is clear that such adjustment is limited to half-turn steps and if intermediate positions of adjustment are desired they must be secured by other means, such as are described hereinafter. A knurled lock nut 24 is provided to secure the casing 23 against rotation when adjusted, and as a further precaution a socket-head screw 25 (Fig. 2) may be provided in the said lock nut itself. As shown in Figs. 2 and 5, the armature 6 completes the magnetic circuit of the E-core transformer to a varying extent, depending upon the air gaps between core and armature, and thus serves as an inductance varying means. The purpose of this will be explained hereinbelow.

The lever 3 is mounted on a tube 26, Figs. 3 and 4, whose central portion is secured to the lever 3, and whose ends are mounted in ball bearings 2'! and 28 carried in tubular guides or bushings 29 mounted in the frame I and held in place by set screws 30. The tube 23 thus allows the lever 3 to turn easily while nevertheless maintaining it properly alined with the rest of the device.

In order to generate torsional resistance proportional to the angle of rotation of the lever 3, a torsion rod 3| is provided. This conveniently is a length of spring wire such as spring-steel wire which passes through tube 26 and is clamped thereto at a single central location by a set screw 32 carried by lever 3. A look nut 33 prevents loosening of said screw. The outer ends of said wire 3| are held by pairs of set screws 34, 35 in bushings 36, 3? which are mounted for rotary adjustment in the frame I through a limited angle.

Each of bushings 36, 31 has an adjusting link 38, 39 respectively secured thereto, these links being located on opposite sides of frame i as shown in Fig. 3. .At their right-hand ends in the Fig. 7 position, the links have slots 43 therein and in each slot is a flanged washer 42, shaped as shown best in Fig. 3. Knurled socket head screws 40 and 4! are provided to secure each link in its adjusted position.

The operation of the invention will now be described briefly. Assuming that the device is secured to the vehicle whose angular acceleration is to be determined, with the torsion rod 3! parallel to the longitudinal axis of said vehicle, it is clear that whenever angular acceleration exists, the lever 3 will tend to remain in its original condition, due to its own inertia, and. thus will apply torsion to the wire or rod 3| proportional to said angular acceleration. The tube 26 merely keeps the lever 3 properly alined, and thereby maintains the cup 9 and the armature 6 in correct relationship to the air gap of the damping magnet and the E-core respectively, without itself providing any torque, as said tube turns freely in its ball bearings 21 and 28.

The spacing of the armature 6 from the poles of said core may be adjusted in steps of one-half the pitch of threads 16 by turning the casing 23, and finer adjustment may then be secured by loosening the screws 40 and M and shifting the links 38 and 39 to control the initial adjustment of the torsion rod 3|, whereupon said links may be held in adjusted position by again tightening the screws 40 and 4|.

The copper cup 9 provides a damping torque due to the eddy currents produced therein by its motion in the strong magnetic field, and in addition provides a certain amount of air damping du to the small clearance of the cup over the pole piece [4 of core H], which restricts the freedom of flow of the air into and out of said cup.

The inductances of the windings on the E-corc are varied by the relative positions of the armature B with respect to the ends of said core, and this variation may be utilized to control the output frequency of an oscillator in which said windings are incorporated, and which thus may emit frequency modulated signals indicative of the acceleration that produces the variations.

Obviously many modifications and variations of the present invention are possible in the light of the above teachings. It is therefore to be understood that within the scope of the appended clalms, the invention may be practiced otherwise than as specifically described.

What is claimed is:

1. In an angular accelerometer, a frame, a lever, a tubular shaft transverse to the lever and secured to said lever, anti-friction bearings mounted in the frame and supporting the ends of said shaft for free rotation, means housed within said shaft and secured to the lever at an intermediate point and having its ends secured to the frame, to generate torsional resistance upon pivotal motion of the lever, inductance varying means carried by one end of the lever, and motion damping means carried by the other end thereof.

2. In an angular accelerometer, a frame, a lever, a tubular shaft transverse to the lever and secured to said lever, anti-friction bearings mounted in the frame and supporting the ends of said shaft for free rotation. a spring housed within said tubular shaft and secured to the lever at an intermediate point and having its ends secured to the frame, to generate torsional resistance upon pivotal motion of the lever, inductance varying means carried by one end of the lever, and motion damping means carried by the other end thereof.

3. In an angular accelerometer, a frame, a lever supported in said frame to pivot freely about an axis transverse to said lever, said lever having at one end an armature or" magnetic material, an open-magnetic circuit core carried by the frame with the open side thereof near and variably partially closed by said armature, said core having windings thereon, whereby the inductances of said windings are varied upon pivotal deflection of the lever, means for adjusting the position of said core to vary the spacing between said core and said armature, torsion generating means connected to said lever and to said frame, and magnetic motion damping means carried by the other end of the lever.

4. In an angular accelerometer as defined in claim 3, additionally a tubular shaft constituting the pivotal support of the lever, said shaft being secured to the lever, and anti-friction bearings mounted in the frame and supporting the ends of said shaft for free rotation.

5. In an angular accelerometer as defined in claim 3, additionally a tubular shaft constituting the pivotal support of the lever, said shaft being secured to the lever, and anti-friction bearings mounted in the frame and supporting the ends of said shaft for free rotation, the torsion generating means comprising a spring passing through the bore of the shaft.

6. In an angular accelerometer, a frame, a lever mounted in said frame to pivot about an axis transverse to said lever, torsional resistance generating means comprising a spring having a portion secured to the lever adjacent said axis,

bushings mounted to turn in opposite sides of said frame, means securing the ends of the spring to the respective bushings, an adjusting link secured to each bushing for turning said bushing, and means for securing the links in their adjusted positions.

7. In an angular accelerometer as defined in claim 6, additionally a tubular shaft transverse to the lever and secured thereto, said spring passing through said shaft, and anti-friction bearings mounted in the frame and pivotally supporting the ends of said shaft.

8. In an angular accelerometer, a frame, a lever supported in said frame to pivot freely about an axis transverse to said lever, said lever having at one end an armature of magnetic material, a tubular shaft constituting the pivotal support of said lever, said shaft being secured to said lever, anti-friction bearings mounted in said frame and supporting the ends of said shaft for free rotation, a core constituting an open References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 2,032,381 Stoutenburgh Mar. 3, 1936 2,302,670 Buchanan Nov. 24, 1942 2,310,213 Buchanan Feb. 9, 1943 2,371,040 Fisher Mar. 6, 1945 2,398,666 Reason Apr. 16, 1946 2,487,793 Esval et a1 Nov. 15, 1947 2,498,118 Weiss Feb. 21, 1950 

